Tang, Sharon Shuk Lan; (2003) Phytochemical and biochemical investigations of Ochna macrocalyx and Bupleurum fruticosum - Searching for NF-κB inhibitory compounds. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

As part of a continuing search for natural product NF-κB inhibitors, the medicinal plants Ochna macrocalyx and Bupleurum fruticosum were selected for phytochemical and biochemical investigations. Ochna macrocalyx compounds were additionally tested for antibacterial and cytotoxic activity. The transcription factor NF-κB regulates the expression of genes involved in the immune and inflammatory responses. Ochna macrocalyx Oliv. (Ochnaceae) is a medicinal Tanzanian tree used for gastrointestinal and gynaecological disorders, which was collected during an ethnobotanical study. Fractions of the crude ethanolic extract inhibited NF-κB at 200 μg/ml in an electrophoretic mobility shift assay. Fractionation of the extract and compound isolation were performed using Sephadex LH-20, silica gel (thin layer, vacuum liquid and flash chromatography) and reverse phase C-18 (in HPLC). Compounds were identified using 1- and 2-D 1H and 13C NMR, FAB and El mass spectroscopy. Six distinctive biflavanoidal compounds were isolated from the bark - two isoflavanone dimers, one of which is new, and four chalcone dimers. None of the isolated compounds showed NF-κB inhibitory activity in an IL-6 luciferase reporter gene assay, used with HeLa cells. Antibacterial broth dilution minimum inhibitory concentration assays were performed with three strains of multi-drug resistant Staphyloccocus aureus, and two of the compounds calodenin B and dihydrocalodenin B showed good antibacterial activity. In cytotoxicity assays (using MTT reduction) against MCF-7 breast cancer cells, calodenin B showed cytotoxic activity (IC50 = 7 ± 0.5 μM). Bupleurum fruticosum L. (Umbelliferae) is a shrub distributed in the Mediterranean area and has been traditionally used as an anti-inflammatory and antiseptic. The ethyl acetate extract of the aerial parts at 100 μg/ml strongly inhibited NF-κB in the IL-6 luciferase assay. Bioassay guided fractionation led to the isolation of three related phenylpropanoids, two of which also showed good activity with IC50S of approximately 30 μM for both compounds.

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